The present invention relates to a data recording/reproducing device for recording or reproducing data (information) by an edge recording method, and more particularly to a data recording/reproducing device capable of performing re-synchronization to correct synchronization on a data recording area.
In recent years, data recording by the so-called edge recording method, which is suitable for high density recording, has been adopted in the field of optical disk devices or the like.
The edge recording method is a data recording method which records or reproduces data in such a manner that the positions of a leading edge and a trailing edge of a pulse signal of a signal pulse are significant. More specifically, the edge recording method records or reproduces data in such a manner that the leading edge and trailing edge of each of the signal pulses obtained by converting data into a run-length limited code correspond to the edge positions of each of the status transition patterns or pits formed on a recording medium. In data reproduction by the edge recording method, it is important to have precise synchronization.
In data recording by the edge recording method, as the case may be, the interval (pit length) between the leading edge and trailing edge of each of the pits, which can be formed by irradiating an optical disk with laser light, does not have a desired length but varies owing to thermal capacitance of the recording medium, changes in a recording condition, etc. For example, if a pit is formed after a lengthy blank, the position of the leading edge can be displaced to a lagged position. If a blank is formed after a lengthy pit, the position of the trailing edge can be displaced to the lagged position. The presence of such displacement causes a change in the relative positional relationship between the leading edge data and the trailing edge data which are detected during reproduction, thus making it impossible to reproduce the recorded data accurately.
The above problem applies to the status transition pattern other than the pits, e.g. recording domains.
In order to solve such a problem, JP-A-62-8370 proposes a method which can absorb or correct deviations from the normal lengths of the recording pits which are due to the property of a recording medium or a change in the recording condition. In this method, in order to detect the deviation from the normal pit length, with the leading edge and trailing edge of the recording pit corresponding to the same demodulation pattern (SYNC pattern), a time difference between two SYNC pattern detection signals resulting from the leading edge and the trailing edge during reproduction is detected by a time difference detector circuit composed of a delay device having plural taps with a fixed delay time interval and a flip-flop.
This prior art, however, has the following defects. Namely, the prior art pays attention to the synchronization signal recorded at the position indicative of the start of an area where any information is recorded, but does not take into consideration re-synchronization in the same area. More specifically, a change in the pit length is detected and corrected only at the head of each sector. Thus, if the recording medium property or recording condition in the first half of the sector is different from that in the second half thereof, as described above, the pit length will vary to provide an appreciable deviation from its normal length, thereby providing an error in the detected signal. More disadvantageously, the error will persist owing to the nature of demodulation. To obviate this, it is essential to have re-synchronization at any suitable position in a data area to stop the persistence of an error.
In this case, as described above, the time relationship between the signal reproduced from the leading edge of a pit or recording domain and that reproduced from the trailing edge thereof will shift undecidedly. The synchronization signal used to collate the time base of the former with that of the latter should be detected using either one of them. Further, it should be discriminatable as a synchronization signal in any data area where any information is to be recorded.